Method for producing, separating, and purifying plutonium



June 22, 1965 G. T. SEABQRGj Em. 3,190,804

METHOD FOR PRODUCING, SEPARATING, AND PURIFYING PLUTONIUM Filed D60. 27,1945 4 Sheets-Sheet 1 Glenn 7.' Jeabory rf/zar C Zc//z( Josep/z ZlfKennedy June 22, 1965 G. T. SEABORG ETAL METHOD FOR PRODUCING,SEPARATING, AND PURIFYING PLUTONIUM Filed Dec. 27. 1945 4 Sheets-Sheet 2June 22, 1965 G. 1'. SEABORG ETAL 3,190,804

METHOD FOR PRODUCING, SEPARATING, AND PURIFYING PLUTONIUM Filed Dec. 27,1945 4 Sheets-Sheet 3 JVA/0 l M 270 rnegi June 22, 1965 G. r. sEABoRGETAL 3,190,804

METHOD FOR PRODUGING, SEPARATING, AND PURIFYING PLUTONIUM Filed Dec. 27.1945 4 sheetssheet 4 Vtion.

United States Patent() $0,894 METHD FOR PRDUCING, SEPARATING, ANDPURIFYHNG PLUTGNIUM Glenn 'I'. Seaborg, Chicago, Ill., Joseph W.Kennedy, Santa Fe, N. Mex., and Arthur C. Wahl, Berkeley, Calif.,assignors to the United States of America .asrepresented by the UnitedStates Atomic Energy Commission Filed Dec. 27, 1945, Ser. No. 637,434 4Claims. (Cl. 176-16) This invention relates to a new chemical element ofatomic number 94, to novel isotopes, compounds and compositions thereof,and to methods -for producing, separating, and purifying same.

The term element 94 is used throughout this speciiication to designatethe element having atomic number 94. Element 94 is also referred to inthis specilication as plutonium, symbol Pu. Likewise, element 93 meansthe element having atomic number 493, which is also referred to asneptunium, symbol Np. Reference herein to any of the elements is to beunderstood as denoting the element generically, whether in its dreestate, or in the form of a compound, unless otherwiseindicated by thecontext.

The apparent discovery of transuranic elements was rst announced byEnrico Fermi in y1934. At that time, Fermi stated lthat the bombardment.of uranium with neutrons gave .beta activities vwhich `he attributed totransuranic elements of atomic number 93 and possibly higher. From 1,934to l1938 other workers, notably Hahn and 'Curie extended this Work. Butin 1939, Hahn discovered that the elements which he .and others hadbelieved to be transuranic elements `were in fact radioactive elementsof intermediate atomic weights produced by the ssion -of uranium. Hahnsresults were subsequently conrmed and a great many other `lissionproducts in addition to `those first found by Hahn were discovered andidentied. Such products were all of lower atomic 'weight than uranium,generally of atomic number in the middle of the periodic system.

So yfar as is kn-own, :prior to about lune 1940, no positive evidencewas [found indicating the existence yof any transuranic element.However, in June 1940, E. McMillan and P. Abelson published in thePhysical fReview, 57, 11185 (1940) `their discovery that a 2.3 dayactivity produced by the bombardment of uranium with neutrons was anisotope .of element 93, probably 93239. Although `it was assumed thatthe initial product of the beta decay tof the 93 lisotope of `2.3 dayhalf-life would be a nucleus of atomic number 94, there was no proofthat any such 94 nucleus could have more than an ephemeral existencebefore undergoing spontaneous disintegra- McMillan and Abelson found novevidence of the production of any daughter product from their 93isotope, and, infact did not .even obtain the '93 isotope itself in pureor useful form.

The present invention relates to transuranic isotopes other than the95239 isotope of `McMillan and Abelson, and particularly `to the variousisotopes of a new element 94.

One aspect of lthe present invention relates to novel methods `for theproduction of element 94. An object of this phase of the invention is toprovide `processes [for the production of element 94 from uranium vbynuclear reactions. A further object of Vthis phase of the `presentinvention is to provide processes for the production of various isotopesof element 94 by nuclear reactions initiated by the bombardment ofnatural uranium by subatomic particles. The neptunium isotopes A93238and 93239 may be produced by the bombardment ,ofuranium with high energydeuterons. The uranium to be bombarded may be the pure isotope 92238 butis conveniently natural uranium, which contains over 99 percent of thisisotope. The uranium may be metallic uranium, an oxide such as U3O8, oryany other desired uranium compound. The deuterons should have energiesof at least l0 m.e.v. (million electron lvolts), and preferably energiesof 14-16 m.e.V. or higher. The Visotopes 93238 .and 93239 are believedto be formed by the following nuclear reactions:

92239 .L, 93239 23 min.

In accordance with Vthe present invention it has been discovered thatthe decay products of the short lived beta emitting isotopes ofneptunium are Vlong lived alpha Vemitting isotopes o f plutonium. Thesedecay reactions may 'be represented as follows:

2.0 days 2.3 days -24, 000 yrs.

Since the decay of neptunium to plutonium takes place both during andafter bombardment of uranium with deuterons or neutrons, the percentageof plutonium in the transuranic Vfraction of the product can becontrolled by varying the bombardment-time, the time -of aging afterbombardment, or both. Thus, in the deuteron bombardment of uranium, thetransuranic fraction of isotopes of mass 238 -will be predominantlyplutonium after live days of bombardment or after one day orfbombardment followed by two days aging. Similarly, in the neutronbombardment of uranium, the .transuranic fraction of the product will bepredominantly plutonium ,after six days of bombardment vor .after twodays of bombardment followed `by two days aging.

For the production and recovery of plutonium, it is preferred to employa total time of bombardment plus aging such that at least percent of thetransuranic fraction of the product consists of plutonium. Examples ofVminimum bombardment and aging times to accomplish this end in theneutron bombardment of uranium are shown in the following table:

TABLE I Days of bombardment Days of aging Although the desired.plutonium concentration in the transuranic 4fraction of the product maybe obtained by suilicient bombardment time alone, it will be evidentthat a nite aging time will necessarily ensue before the plu- 'toniumcan be separated from the bombarded product.

In the present specification and claims, therefore, it is postulatedthat the bombarded product is always aged, and that .the plutoniumconcentration in the transuranic fraction of the product is controlledby the total time of bombardment plus aging.

The production of plutonium by deuteron bombardment of uranium followedby aging of the bombarded product will be further illustrated by thefollowing examples:

Example 1 Uranium oxide, comprising predominantly U30, with a minoramount of U03, was subjected to 230 microampere hours bombardment with15 m.e.v. deuterons from a cyclotron. Neptunium was separated from thebombarded mass by chemical means, using cerous fluoride carrierprecipitations to obtain a product suitable for radioactive analysis forneptunium content. The amount of neptunium present at the end of thebombardment was then determined by analysis of the beta radiation decayof the product. The yield of neptunium was found to be approximately 28euries per ampere hour of bombardment. This neptunium was transformedinto a substantially equal mass, and equivalent number of curies, ofplutonium after aging for 30 days.

Example 2 Uranium metal was subjected to a short bombardment with 15m.e.v. deuterons, and the neptunium was separated from the bambardedmaterial by chemical means to obtain a product containing neptunium asthe only beta emitting radioactive element. The quantities of the 2.0day isotope 93238 and the 2.3 day isotope 93239 present at the end ofthe bombardment were then determined by analysis of the radioactivedecay of the total 93. The yields were found to be 36.2 micrograms of93233 and 320 micrograms of 93239 per ampere hour of bombardment. Afteraging for 60 days, the yields of 94238 and 94239 derived from theseparated neptunium were thus approximately 36.2 micrograms of 94233 and320 micrograms of 94239 per ampere hour of bombardment.

Example 3 to 94239. The yields of 94233 determined in this manner werefound to be as follows:

Yield o 94238 (micro- Deuteron Energy (million electron volts) grams perampere hour l bombardment) Plutonium has been successfully produced inaccordance with the present invention by the bombardment of uraniu-mwith an external source of neutrons, such as a deuteron-berylliumsource, adjusting the bombardment and aging times to secure a product inwhich the transuranic fraction is substantially all plutonium, andthereafter isolating the plutonium. Much higher production rates areobtainable, however, by the use of neutronic reactors of the typedescribed in co-pending application Serial No. 568,904 of E. Fermi andL. Szilard, iiled December 19, 1944, now U.S. Patent No. 2,708,656,granted on May 17, 1955. In such reactors a ssionable isotope, such asU235 in natural uranium, undergoes iission and releases fast neutrons inexcess of the neutrons absorbed in the fission process. The fastneutrons are slowed down to approximately thermal energies by impactswith a moderator such as graphite or deuterium oxide, and the resultingslow neutrons (energies of 0-O.3 electron volt) are then absorbed byU235 to produce further rission and by U238 to produce U239 which decaysthrough 93239 to 94239. This self-sustaining chain reaction releasestremendous amounts of energy, primarily in the form of kinetic energy ofthe fission fragments. With such reactors the maxi-mum reaction rate forsteady lstate operation is determined by the maximum rate at which theheat of reaction can be removed. The rate of production of plutonium insuch reactors may thus be equated, approximately, to the power output ofthe reactor, and amounts to about 0.9 gram of 94239 per megawatt daywhen operating with sufficient bombardment and aging times to permittotal decay of 93239 to 94239.

It is to be understood, of course, that the above examples of methodsfor the production of 94239 and 94239 are merely illustrative and do notlimit the scope of this phase of the present invention. Sources of highenergy deuterons or low energy neutrons other than the particularsources of the examples may be employed, and various modilications ofthe operating procedures may also be used. Equivalent nuclear reactionsmay be utilized, as for example, the bombardment of uranium with anysub-atomic particle of suitable energy to produce a beta-emittingneptunium isotope, with control of bombardment and aging times to permitrecovery of a transuranic fraction comprising essentially plutonium.

Further aspects of the present invention relate to methods for theseparation and purification of plutonium, and especially to methods forthe separation and decontamination of the plutonium contained in massesof deuteron bombarded uranium or neutron bombarded uranium.

One phase of the present invention which is especially useful inplutonium recovery processes relates to methods for the control of thestate of oxidation of plutonium. An object of this phase of theinvention is to provide means for attaining a plurality of oxidationstates of plutonium. Another object of this phase of the invention is toprovide methods for oxidizing plutonium from a lower to a higher valencestate, and for reducing plutonium from a higher to a lower valencestate. A further object is to provide means for stabilizing lower andhigher oxidation states of plutonium in aqueous solutions of plutoniumions. Additional objects and advantages of this phase of the presentinvention will be evident from the following description.

In accordance with the present invention it has been found thatplutonium is chemically unlike osmium in many respects, and is probablya member of a second rare earth group, the actinide series. It hasfurther been discovered that plutonium, unlike a number of other membersof this series, possesses a plurality of valence states. Plutonium hasat least four valence states, including +3, +4, +5, and +6. In 0.5M.-1.0 M. aqueous hydrochloric acid the oxidation-reduction potentialsare of the following magnitudes:

As may be seen from the above couples, the stability of the higheroxidation states is dependent on the hydrogen ion concentration. Inmoderately acidic solutions the Pu+5 ion is generally very unstable, anddisproportionates to Pu+4 and Pul-G. The Pu+4 ion is capable 0fdisproportionating to the Pu+3 ion and the PuO2+2 ion, and in diluteaqueous hydrochloric acid this disproportionation may take place to aconsiderable extent. The Pu+4 disproportionation is opposed, however, byincrease in hydrogen ion concentration and by the presence of ions whichtend to complex or otherwise stabilize the Put4 ion. The effect ofadditional ions in hydrochloric acid solutions is illustrated by thefollowing potentials for the Pu+3Pu+4 couple:

1.0 M. HC1 0.97 V. 1.0M.HC1 0.1 M. H3PO4 0.80 V. 1.0 M. HCl l.0 M. HF0.53 v.

Generally the anions of slightly ionized acids tend to complex the Pu+4ion to a much greater extent than the anions of highly ionized acids.Thus, Pu+4 is only slightly complexed by C104-, Cl, and N031 it scomplexed to a much greater extent by S04-2; and it .is very stronglycomplexed by POKE, F, C21-1302, and C2052.

In addition to the complexing effect of the anions of the acids employedas solvents for plutonium, certain of these acids may also serve asoxidizing agents. However, at room temperatures, or moderately elevatedternperatures, and in the absence of oxidation catalysts, the rate ofoxidation by the acid is often so low that this effect may be ignored.Thus, the Pu+4 ion is stable for considerable periods of time inperchloric acid, although under proper conditions, the latter is-capable of oxidizing Pu+4 to Pu02+2. It is therefore desirable tocontrol the state of oxidation of the plutonium by Ythe use of oxidizingagents and reducing agents which have rapid reaction rates under theconditions employed for nprocessing the solutions.

1.0 M. HCl 1.0 v. 1.0 M. HNO3 1.1 v. 1.0 M. HESO., y 1.3 V.

Oxidizing agents having adequate oxidation-reduction potentials for usein such solutions may be chosen by reference to tables such as the tableof standard oxidationreduction potentials given in the Reference Boo'kof lnorganic Chemistry by Latimer and Hildebrand (The MacMillan Company,New York, 1934).

It is generally desirable to effect puriiication and concentration ofplutonium in nitric acid solutions. Examples of oxidizing agents for usein such solutions are bromates, permanganates, dichromates,silver-catalyzed peroxydisulfates, and ceric compounds. To effect theoxidation, a quantity of oxidizing agent at least equivalent to theamount of plutonium is added to the solution, and the resulting mixtureis digested at a moderately elevated temperature for a suiiicient periodof time to insure complete oxidation of the plutonium. In most cases,this digestion may suitably be effected at 60-80 C. for -60 minutes. Inorder `to maintain vthe plutonium in the hexavalent state forconsiderable periods of time `after oxidation, it is desirable to employan excess of oxidizing agent to serve as a holding oxidant. This isespecially true if an acid solution is to be processed in ferrous metalequipment, or under other conditions permitting subsequent reduction ofthe plutonium.

Neptunium may be oxidized by any of the oxidizing agents mentionedabove, without/the necessity of digestion at an elevated temperature.This greater rapidity of oxidationof neptunium at low temperatures maybe utilized to effect preferential oxidation of neptunium withoutsubstantial oxidation of plutonium. The preferred oxidizing agent forthis purpose is the bromate ion. At temperatures of 15-25 C. neptunium'may be substantially completely oxidized by alkali metal bromates innitric acid solutions, which contain ions such as S042 ions to complex|4 plutonium, without appreciable oxidation of plutonium to Ithehexavalent state. There is lsome evidence that bromate oxidation ofplutonium may be catalyzed by cerium, and it is therefore desirable toVeffect the preferential oxidation of neptunium in ceriumfree solutions.

For the Vreduction of plutonium, reducing agents of adequatepotentialmaybe selected `by reference to tables `of standard potentials such asthe table `previously referred to. The reduction may suitably beeffected by digestion at room temperature or slightly elevatedtemperatures. Digestion for 15 to 60 minutes at 15 to 35 C. willgenerally be satisfactory.

For the reduction fof PuO2+2 or Pu+4 to Pu+3, the reducing agent shouldhave an oxidation-reduction potential substantially more positive thanthe oxidation-reduction potential of the Pu+3 Pu+4 couple in thesolution employed. Thus, in 1.0 M. HCl an active reducing agent having apotential more positive than -0.97 v. will be required, and in 1.0 M.HNOS, a potential more positive than -0.92 V. will be necessary. Inorder to main-tain the plutonium in the |3 valence state for appreciableperiods of time, it is desirable to maintain an excess of the reducingagent in solution.

.In order 4to reduce PuOZ-l'2 to VPui'4 Without reducing Pur4 to Pu+3,it is desirable to vemploy an active reducing agent 'having an`oxidation-reduction potential substantially more l.positive than `theoxidation-reduction potential ofthe Pu+4-ePuO2+2 couple, andsubstantially more negative than the oxidation-reduction potential ofthe Pu+3 lu+4 couple, in the solution used. A wider selection ofvreducing agents of the desired potential will be available for use insolutions containing ions which complex the Pu+4 ion than are availablefor use in solutionsl which are substantially free from complexingeffects. Thus, in Y1.0 M. HC1 and 1:0 M. HCl-1.0 M. HF, theoxidation-reduction potentials are approximately:

f" It maybe seen that in the solution containing tluoride Vion reducingagents such as hydrogen peroxide and ferrous iron, which haveoxidation-reduction potentials of 0.68 v. and 0.74 v. respectively, willreduce PuO2+2 only to Pu+4; whereas in the solution without Vfluorideion to complex'the 'Pu+4 ion, Vthese reducing agents will tend to reducethe vplutonium to the +3 state. A reducing agent such as sulfur dioxide,having an oxidation-reduction potential of 0.14 v, will tend to reducethe plutonium to the `|3 state in either solution.

When employing the preferred solutions iof plutonium in aqueous nitricacid, Vthe reduction of Pu02+2 to Pu+A1 is preferably effected in thepresence of a complexing ion, employing reducing agents havingoxidation-reduction potentials of the same magnitude as hydrogenperoxide and ferrous iron. However, it is also possible to use strongerreducing agents such aszsulfur dioxide if any excess reducing agent isremoved or destroyed after the initial reduction is effected. In anycase, if Pu+4 is desired, the hydrogen ion concentration should besufliciently high to oppose the disproportionation fof lEuJf4 to Pu+3and PU2+2- For this purpose, it is desirable to employ solutions havinga pH not substantially above 2, and preferably considerably below 1. Inthe case of aqueous nitric acid solution, it is generally desirable tomaintain a free acid concentration of at least 1 M.

It will be apparent that the considerations discussed above will alsoapply to the oxidation of Put3 to Pu+4, without oxidizing Pu+4 toPuO2+2, by the use of oxidizing agents having potentials intermediatethe potentials of .the two plutonium couples.

The plutonium oxidation and reduction processes described above may beemployed, if desired, for the simultaneous oxidation or reduction ofboth neptunium and plutonium. Such simultaneous oxidation or reductionwill be attained provided equilibrium is reached. As previously pointedout, however, differential reaction rates may be utilized to attain oneoxidation state forneptunium and another oxidation state for plutonium.

The solutions of plutonium ions of the various valence states describedabove are useful for the electro-deposition of plutonium, for theprecipitation of plutonium compounds while leaving contaminatingcompounds in solu- 7 tion, and for the precipitation of contaminatingcompounds while leaving plutonium in solution, as will be discussed indetail in the description of other phases of the present invention.

The oxidation state of plutonium in aqueous solutions of the variousplutonium cations may be determined in accordance with methods commonlyused for the determination of the Valence state of other metals insolution. Thus, the total plutonium in solution may be determined byquantitative gravimetric or radiometric analysis, and the percentage ofany particular ion may then be determined by a suitable differentialanalysis, such as quantitative oxidation or reduction, polarographicanalysis, or the like. Spectrophotometric analysis is especiallyadvantageous for determining qualitatively or quantitatively the variousplutonium ions in solution, in View lof the sharp characteristic peaksin the absorption spectra for the different valence states.Representative molar extinction coeicients for the Pu+3, Pu+4, andPuOZi'2 ions in aqueous inorganic acid solutions are given in thefollowing tables:

TABLE 2 8 tion procedure for the selective extraction of uranyl nitratefrom aqueous compositions containing uranyl nitrate, uranium lissionproducts, and plutonium.

An additional object is to provide an ether extraction process for thetreatment of neutron irradiated uranyl nitrate hexahydrate or deuteronirradiated uranyl nitrate hexahydrate to separate an ether phasecontaining the major portion of the uranyl nitrate from an aqueous phasecontaining plutonium and uranium fission products.

Other objects and advantages of this phase of the present invention willbe evident from the following description.

If uranium is subjected to neutron or deuteron bombardment, even forprolonged periods of time, the bombarded product comprises predominantlyunconverted uranium with only very low concentrations of uranium ssionproducts and plutonium. A desirable preliminary step in the recovery ofthe plutonium from such material consists in separating the majorportion of the unconverted uranium, thus reducing the bulk of theplutonium Pu+3 in 1 M. HCl

waveiengthinii 4,260 4,560 4,740 5,050 5,620 5, 010 6, 060 s, 000 9,000

Molar extinction coelncient 12.0 4.7 4.0 3.5 37.4 37.9 15.0 15.0 18.9

TABLEa 1 u+4 in 1 M. rrNos waveiengthinn 4,040 4,220 4, 450 4,760 5,0205,460 6,000 7, 060 5,000 8,550

Molar extinction TABLE4 Pu+4 in 1 M. Hzsoi waveiength 111A 4, 000 4,3504,610 5,480 6,640 7,200 s, 140 s, 510

Moiarexuneuon @06111016116 20.2 28.5 85.2 20.0 39.6 21.0 27.1 14.3

TABLEs Puo2+2 in 1 M. HNOS waveiengthma 4,590' 4700i 5,060 5,220' 6,240]2,310 9,580 0,870 Monrenmcnon @einem 15.0 14.0* 14.0 14.01 10.0 171.023.0 17.0

The particular oxidizing and reducing agents, processes, and solutionsdiscussed above are merely illustrative and are not to be construed aslimiting the scope of this phase of the present invention. Otheroxidizing and reducing agents having the required potentials may beutilized instead of those specifically mentioned, and the procedures maybe modied in numerous respects, as will be evident to those skilled inthe art.

A further aspect of the present invention relates to the separation ofplutonium from uranium, and especially to the separation of plutoniumfrom neutron irradiated uranium or deuteron irradiated uranium.

An object of this phase of the invention is to provide a method forselectively separating uranium from aqueous compositions containinguranium and plutonium.

Another object of this aspect of the invention is to provide a methodfor extracting the bulk of the uranium from aqueous compositionscontaining uranyl nitrate and plutonium.

A further object is to provide an organic solvent extracfraction andconcentrating the plutonium with respect to the remaining uranium.

In accordance with the present invention it has been discovered thatplutonium in an oxidation state not greater than +4 may be maintained inan aqueous phase while extracting hexavalent uranium from said aqueousphase into an organic solvent. For this purpose any of the organicsolvents which are known to dissolve uranyl compounds may be employed.The preferred class of solvents comprise normally liquid organicsolvents which are substantially immisciole with the aqueous solution tobe extracted and which contain at least one atom capable of. donating anelectron pair to a coordination bond. Compounds containing oxygen donoratoms, such as alcohols, alkyl ethers, glycol ethers, ketones, andnitrohydrocarbons, are particularly desirable solvents. For theextraction of hexavalent uranium from tetravalent plutonium, it ispreferred to employ an ether, and particularly diethyl ether, as thesolvent. For the extraction of hexavalent uranium from trivalentplutonium, it

phase.

aqueous fphase of smaller volume comprising the original water ofcrystallization, a minor portion of the uranyl nitrate, andthe `bulkofthe uranium fission products and plutonium.

'Instead of directly extracting crystalline hexahydrate, the bombardedmaterial may ir'st be dissolved in nitric acid or other suitable aqueoussolvent. Similarly, bornbarded uranium metal, uranium oxides, or otheruranium compounds may be dissolved in aqueous inorganic acids to formsolutionssuitable for extraction. It is generally plutonium in theresulting solution may then be stabilized in the +3 or -|4 Voxidationstate by means of reducing agents which have insucient potentials toreduce the hexavalent uranium.

:Forthe extraction-of uranyl nitrate from solutions containingtetravalent plutonium, it is desirable to have a high initial uranylnitrate concentration in the aqueous phase; suitable solutions containat least 30 `percent by weight of uranyl nitrate hexahydrate, andpreferably considerably higherconcentrations. The uranyl nitratesolutions .may suitably be concentrated until saturated with .respecttothe lhexahydrate or even to the point Where the .entire mass willsolidify, on cooling, as crystalline hexahydrate. Other soluble saltsshould be excluded fromthe aqueous solution, insofar asrpracticable, inorder to prevent salting-out the plutonium into the organic Similarly,excessive acidconcentrations should be avoided in order to minimizeextraction of plutonium by the organic solvent.

It has further been discovered, in accordance with the presentinvention, that trivalent plutonium has muchless -`tendency to extractinto the organic phase than tetravalent plutonium. Thus, high acidconcentrations andhig'h concentrations of salting-out-agents may beemployed to increase the eciency of the uranium extraction withoutda-nger of excessive extraction of trivalent plutonium. The

preferred salting-out agents comprise inorganic salts having highsolubility in the solution to be-extracted, low

solubility in the -rextract phase, and a common ion with Vrespect to thecompound being extracted. Thus, for the extraction of uranyl nitrate,thefollowing nitrates are suitable salting-out agents:

NaNO3 'CSNOQZ KNO3 sfuma)2 LNOS Mg(NO3)2 NH4N0, ramos), MH(NO3)2 AMNOFJSThe concentration of salting-out agent which is desirable in anyparticular case will depend on the valence of the cation andtheconcentration of the common anion due to freeacid in the solution. Inthe case of 1 N. nitric acid solutions, it is desirable to employ aconcentration of a univalent nitrate of at least 3 M. and preferably5-10 M. Equivalent concentrations of polyvalent nitrates may be employedat the same acid concentration, andthe salt concentration may suitablybe increased or descreased with decrease or increase of the acidconcentration.

In carrying out the process of this phase of the present invention,previously 1known extraction procedures and apparatus may be employed.The extraction may -be e-ffected by batch, continuous batch, batchcounter-current, or continuous counter-current methods. Batch operationis generally preferred for the extraction of solutions ypreferred to.employ nitric acid for this purpose, in order :to obtain ,directly asolutionof hexavalent uranium. The

containing tetravalent plutonium, whereas continuous counter-currentoperation may advantageously be applied to the extraction of solutionscontaining trivalent plutonium. A two-stage batch process, employing ineach stage from 2 to 10 volumes of solvent per volume o-f material to beextractedor an-equivalent counter-current process, Will usually effectadequate preliminary separation of uranium to permit eiiicient operationof subse- `quent chemical methods for plutonium recovery. A greaternumber of batch stages or greater quantities of solvent incountre-cnrrent operation may, however, be employed if desired.

This phase of the present invention will be further illustrated by thefollowing specificexamples:

Example 4 Uranyl nitrate hexahydrate containing tetravalent plutonium intracer concentration was extracted with approximately 28 times itsvolume of'ethen-and the aqueous layer was 4re-extracted with Va quantityof ether equal to that used in the Afirst extraction. The aqueousraiiinate Was then acidiiied with about 1.5 times its volume of 1'6 N.aqueousnitric'acid, and the resulting nitric acid solution was extractedwithapproximately 20times its volume of ether.

The other extracts and the tinal aqueous rainate were analyzed forplutonium by a `precipitation procedure designed -to leave uraniumunprecipitated and to yield lprecipitates containing-plutonium asitheonly alpha-active component. Radioactive analyses of 'the precipitatesshowed the aqueous raiiinate tocontain-approximately 89 percent of the`total aloha radiation, whereas the ether .extracts containedonly l'lpercent. On the other hand, analysis of the aqueous raiinate foruranium'by evaporation-and ignition to U30?, showedthat it containedlless than 0.3 percent of the original uranium.

Example 5 0 hours bombardment of beryllium with 12 m.e.v. deuterons overa period of 20 days, was aged for S days prior to extraction with ether.Approximately 700pounds of the ,bombarded and aged material wasextracted with about 84 'gallons of diethyl ether. The aqueous ,phasewas evaporated to reduce the water content to'that of uranyl nitratehexahydrate, and about 490 :pounds `of 4recrystallized hexahydrate wasthusobtained. The recrystallized material was then re-extracted with10.8 gallons of diethyl ether. The aqueous rainate thusy obtained had avolume of approximately L64 gallons and contained approximate- `ly 1.66percent of the original uranium. This solution was analyzed forplutonium and was foundto contain 353 micrograms, corresponding to ayield of 3.5 micrograms per milliarnpere hour of bombardment.

Example' Ammonium nitrate is added as a salting-out agent to a nltricacid solution containing uranyl nitrate, uranium `fission products, andtrivalent plutonium. The concentrations of uranium, nitric acid, andammonium nitrate in the resulting solution are as follows:

M. Uranyl nitrate 1.08 VNitric acid 1.86 Ammoniumnitrate 6.75

alent Water-immiscible organic solvents may be substituted for thediethyl ether and methyl isobutyl ketone employed in the examples, andthe specific procedures employed may be modified in numerous respectswithin the scope of the foregoing description.

A further aspect of the present invention relates to the separation ofplutonium from aqueous solutions, and especially from aqueous solutionscontaining plutonium together with other contaminating elements, such assolutions derived from neutron irradiated uranium or deuteron irradiateduranium.

An object of this phase of the invention is to provide lprecipitationmethods for the separation of plutonium from aqueous solutionscontaining ionic plutonium.

Another object of this aspect of the present invention is to providesuitable precipitation methods for separating plutonium from aqueoussolutions containing plutonium and uranium fission products, and forsimultaneously effecting at least partial decontamination of theplutonium with respect to said uranium fission products.

A further object is to provide carrier precipitation procedures forseparating plutonium from aqueous solutions containing plutonium inconcentrations below the solubility concentration of its most insolublecompound.

Ari additional object is to provide suitable carrier precipitationmethods for separating plutonium with sirnultaneous decontamination,from aqueous solutions containing plutonium in very low concentrationsand containing contaminating elernents in concentrations at least ashigh as for plutonium concentration.

Other objects and advantages of this phase of the present invention willbe apparent from the following description.

Aqueous solutions derived from neutron irradiated uranium or deuteronirradiated uranium may contain, in addition to plutonium, numerouscontaminating elements in concentrations relatively high with respect tothe plutonium concentration. Even after preliminary separation ofunconverted uranium by solvent extraction, or by chemical means, suchsolutions may contain uranium in a concentration considerably exceedingthe plutonium concentration. Solutions derived from unaged irradiatedmaterial may also contain neptunium in substantial concentration. Thecontaminating elements presenting the greatest difficulties in therecovery of plutonium comprise the uranium fission products.

When natural uranium is subjected to bombardment with neutrons ordeuterons, nuclear fission takes place simultaneously with the formationof transuranic elements. Nuclear fission constitutes a breakdown of theheavy nucleus into lighter fragments which are generally very unstableand highly radioactive. Such fragments usually undergo beta-particledisintegration in successive steps, leading ultimately to stableisotopes of higher nuclear charge than the original fragments. In thecase of a neutronic reactor operating with a self-sustaining chainreaction, the number of uranium nuclei undergoing fission is roughlyequivalent to the number undergoing reaction to form transuranicelements. Since the fission products are at least twice the number ofnuclei undergoing fission, aged material from a chain reaction willcontain a greater number of atoms of fission products than of plutonium.

Although some fissions of U238 and U235 is caused by neutrons havingenergies above about 1,000,000 electron volts (l m.e.v.), by far thegreatest proportion of fission products formed in a neutronic reactorare due to the action of thermal neutrons on U235. The fission of U235is predominantly binary, and may be exemplied by the following type ofequation:

Substantially all of the fission fragments have mass numbers within therange 77-158, although small quantities of isotopes of lower and highermass numbers may result from unbalanced binary ssions, ternary iissionsor other reactions of infrequent occurrence. A large majority of thefission fragments comprise a light group of mass numbers 84-106 and aheavy group of mass numbers 12S-150.

The various decay products of the initial fission fragments are referredto herein as fission products. These fission products fall within arange of atomic numbers from about 32 to about 64. The fission productsfrom the light group of fragments have atomic numbers ranging from about35 to about 46; and the fission products from the heavy group offragments have atomic numbers ranging from about 5l to about 60.

The various radioactive fission products have half-lives ranging from afraction of a second to thousands of years. Those having very shorthalf-lives may be eliminated by aging the material for a reasonableperiod before handling. Those with very long halflives do not havesufficiently intense radiation to endanger personnel protected bymoderate shielding. On the other hand, the fission products havinghalf-lives ranging from a few days to a few years have dangerouslyintense radiations Which cannot be eliminated by aging for practicalstorage periods. These products are chiey radioactive isotopes of Sr, Y,Zr, Cb, Ma, Ru and Rh of the light group and Te, I, Cs, Ba, La, Ce andPr of the heavy group.

One method of recovering plutonium from compositions containing any ofthe contaminating elements discussed above is to form an aqueoussolution having a plutonium concentration sufiicient to permit theprecipitation of an insoluble plutonium compound. The recovery ofplutonium as an insoluble precipitate is particularly applicable tosolutions in which any contaminating cations do not form insolublecompounds with the anion to be employed for the precipitation of theplutonium. By proper choice of anions and repeated reprecipitations,plutonium of a high degree of purity may be recovered by this method.

The suitability of various anions for the precipitation of insolubleplutonium compounds will depend on the oxidation state of the plutoniumand on the nature of the aqueous solvent from which the precipitation isto be made. We have found that the anions which are suitable for theprecipitation of an insoluble compound of trivalent or tetravalentplutonium from any solution suitably comprise the anions which may beused to precipitate an insoluble compound of trivalent or tetravalentcerium from the same solvent. In the same manner that the solubility ofthe lower valence states of plutonium parallels that of cerium, thesolubility of hexavalent plutonium corresponds to that of hexavalenturanium.

The following plutonium compounds are insoluble in Water, the terminsoluble being used to designate solubilities of less than 0.01 mol perliter:

Trivalent plutonium:

Fluoride Orthophosphate OXalate Hydroxide (basic nitrates, sulfates,chlorides, etc.) Tetravalent plutonium:

Fluoride Double Fluorides (KPuF, K2PuF6, LazPuFlO, etc.) Oxalate IodateOrthophosphate Hydroxide (basic nitrates, sulfates, chlorides, etc.)Peroxide (basic peroxidic nitrates, sulfates, chlorides,

etc.) Hexavalent plutonium:

Hydroxide (basic nitrates, sulfates, chlorides, etc.)

It is generally desirable to precipitate plutonium compounds from acidicaqueous solutions, and especially from `aqueous inorganic acidsolutions. Representative solubilities of trivalent and tetravalentplutonium compounds in dilute solutions in W ich t'ne plutoniumconcentration is below the solubility concentration of the mostinsoluble solutions of various acids "and of various aeid concentrationsyare given in the following table:

TABLE 6 parts of Will often m in extremely low concentrations. The

utonium'from such solutions, or f romdilute sion product cations whichform soluble products (Solu- 65 Waste solutions or the like, cannotusually be effected by bility in excess of 0.01 mol per liter) in 0.01N.N. nitric recipitation of an insoluble plutoniumcompound. lution of`plutonium contains substantial amounts of contaminatingk elements.Concentration by When precipitatingan insoluble plutonium compoundplutonium compound. Since the plutonium concentrafrom a solutioncontaining uranium vission 'products 01' tion in neutron irradiateduranium is vgenerally substanother contaminatingelements,substantialdecontamination 63 tially below 1% of the Weight of the unreacteduranium, of the vplutonium may be `effected by the utilization of andmay even be less than one part per million anions which form insolubleplutonium compounds but uranium, solutions derived from such materialWhichform soluble compounds with one or more of the contain plutoniucontaminating cations. The following areillustrative isrecovery of pl adirect p If a dilute so acid on the addition of Various anions whichprecipitate tetravalent plutonium.V

ten result in a partial separation of evaooi'ation will insolublecarrier to effect removal of the plutonium from the solution. Theinsoluble carrier may be introduced into the solution as a pre-formedfinely divided solid, but is preferably precipitated directly in thesolution from which the plutonium is to be carried. rlhe mechanism ofthe carrying of plutonium from solution is not fully understood, but itis believed to be effected in some cases by incorporation of plutoniumions into the carrier crystal lattice, in some cases by surfaceadsorption of plutonium ions, and in other cases by a combination ofboth.

The term carrier as used herein and in the appended claims is to beunderstood as signifying a substantially insoluble, solid, finelydivided compound capable of ionizing to yield at least one inorganiccation and to yield at least one anion which constitutes an ioniccomponent of a compound which contains the ion to be carried, saidlatter compound being not substantially more soluble than said finelydivided compound in the same solution. The preferred carriers fortrivalent plutonium comprise compounds having an anion which is capableof forming an insoluble compound of trivalent cerium in the samesolution; and the preferred carriers for tetravalent plutonium comprisecompounds having an anion which is capable of forming an insolublecompound of tetravalent cerium in the same solution.

A large number of carriers are available for carrying plutonium fromsolution in accordance with this phase of the present invention. Thefollowing are representative examples of useful carriers:

It will be apparent that the above compounds constitute plutoniumcarriers in accordance with the definition previously given. Thus,lanthanum fiuoride is capable of ionizing to form a lanthanum cation anda fluoride anion. The latter is an ionic component of the insolublecompounds PuF4 and KPuF5. In an analogous manner, a basic peroxidicthorium nitrate is capable of ionizing to yield a Th+4 cation and NO3-and OCH- anions. The latter anions are ionic components of an insolublebasic peroxide plutonium nitrate.

The ratio of carrier to plutonium to be employed may vary over a widerange depending on the plutonium concentration of the original solutionand upon the effectiveness of the particular carrier employed. Weightratios ranging from 10,000/ l or higher to /1 or lower may be used, butthe ratio will generally fall within the range 1000/1 to 100/1. If a lowratio of carrier to plutonium is desired, an isomorphic carrier ispreferred, i.e. one having a crystalline structure with cation spacingin the crystal lattice such that plutonium ions may be substituted inthe lattice for carrier cations.

It is apparent that different carriers will be required for theisornorphic carrying of plutonium in its different valence states. Forplutonium in the +3 state, cerous and lanthanum compounds are suitableisomorphic carriers. Uranous, ceric, and thorium compounds areisomorphic carriers for plutonium in the +4 state, Whereas uranylcompounds are isomorphic with plutonyl cornpounds (+6 plutonium). It isgenerally preferred to carry plutonium in the +4 state and for thispurpose there may be employed, in addition to the isomorphic carrierslisted above, other carriers of the same range of ionic radii. Desirablecarriers for +4 plutonium comprise those having cations of ionic radiiwithin the range 0.75-

0.97 A., as corrected in accordance with Zachariasens method fordetermining corrected ionic radii (Zeit. fr Kryst. 80, 137, 1932).

1f plutonium is to be carried from a solution containing a large numberof contaminating elements, it is possible that one or more of thecontaminants may be isomorphic with the cations of certain of theplutonium carriers which could be employed. For maximum decontaminationof plutonium in a single carrier precipitation, it is therefore,desirable to choose a carrier cation which is isomorphic with none, orwith the least number, of the contaminating cations known to be present.

Even if there is no isomorphic carrying of contaminants simultaneouslywith the plutonium, some of the contaminating cations may be carried tosome extent by absorption or by other mechanisms. If the contaminants inquestion are dangerously radioactive, such as are most of the uraniumfission products with which plutonium is usually associated, it isdesirable to minimize the carrying of such radioactivity with theplutonium. One method of reducing the amount of radioactivity carried bya carrier precipitate is to introduce into the solution a radioactivelyinert diluent or hold-back carrier, which is an inactive isotope of theradioactive isotope which is to be held back in the supernatant solutionduring precipitation of the carrier. This method is particularlyeffective for reducing the carrying of radioactive isotopes which arecarried by adsorption or other surface saturation type of carrying.Thus, inactive isotopes of the various uranium fission products whichare not isomorphic with the carrier cation may be employed to improvethe decontamination of plutonium when carrying it from solutions derivedfrom neutron irradiated uranium.

The carrying procedure may be effected by any of the known techniquesfor effecting adequate contact of liquids with insoluble solids. In thecase of preformed carriers, the finely divided solid may be agitatedwith the solution, or the solution may be continuously passed throughfixed beds of the carrier. As previously pointed out, however, thepreferred procedure is to precipitate the carrier directly in theplutonium solution. This may be effected by adding the ions in anyorder, but it is generally preferred to add the cation first, and thenthe anion. Mixed carriers may be precipitated, if desired, byprecipitating two or more cations with the same anion, two or moreanions with the same cation, or by co'prccipitating carriers differingin both cation and anion.

When employing any of the above procedures it is desirable to provide anadequate contact time or digestion period to insure adequate carrying ofthe plutonium. This is particularly desirable in the case of isomorphiccarrying or other internal carrying. The digestion may be effected atroom temperature, but it is usually preferred to employ an elevatedtemperature ranging from about 30 C. to a temperature substantiallybelow the boiling point of the solution. Temperatures of 40 to 60 C.will generally be satisfactory, with a contact time or precipitatedigestion time of 10 to 90 minutes, and preferably 30 to 60 minutes. Thecarrier may then be separated from the supernatant solution by anysuitable means, such as decantation, filtration or centrifugation.

The separation of plutonium from aqueous solutions by means of variouscarrier precipitates is further illustrated by the following specificexamples:

Example 7 An 8.6 N. sulfuric acid solution was prepared containinglanthanum sulfate in a concentration of approximately 430 rng. per literand plutonium in tracer concentration. To this solution was added about2.1 times its volume of a saturated aqueous solution of sulfur dioxide,and the mixture was allowed to stand at room temperature for 25 minutesto effect reduction of any hexavalent plutonium. The sulfuric acidconcentration of the resulting solution was about 2.8 N. and thelanthanum sulfate 17 concentration was about 139 mg. per liter. About27% by volume of 48% aqueous hydrouoric acid was then added to thesolution and the resulting lanthanum fluoride precipitate was separatedby centrifuging. Analyses for alpha radiation showed that theprecipitate contained 93% of the plutonium which was present in theoriginal solution.

Example 8 A 0.07 N. sulfuric acid solution was prepared, containingcerous sulfate in a concentration of about 64 mg. per liter andtetravalent plutonium ion in tracer concentration. About 39% by volumeof 48% aqueous hydrofluoric acid was then added and the resulting cerousfluoride precipitate was separated by centrifuging. Analyses for alpharadiation showed that the precipitate contained 92% of the plutoniumwhich was present in the original solution.

Example 9 Lanthanum nitrate was added to a 1.0 N. HNO3-0.1 M. H3130.;solution containing tetravalent plutonium to produce a lanthanum ionconcentration of approximately 0.15 g. per liter. The solution was thenheated to 70 C. and was neutralized with sodium hydroxide until justalkaline to litmus. The resulting slurry was digested at roomtemperature for two hours, with agitation, and the lanthanum hydroxideprecipitate was then separated by centrifuging. Radioactive analyses ofthe original solution and of the precipitate showed that 97% of theplutonium was carried by the lanthanum hydroxide.

Example 10 Thorium nitrate tetrahydrate was added to a 0.1 N. nitricacid solution containing tetravalent plutonium in tracer concentrationto produce a thorium ion concentration of approximately 2 g. per liter.Hydrogen peroxide in the form of a 3% aqueous solution was then added ina concentration. Substantially in excess of the equivalent thoriumconcentration, and the resulting thorium peroxide precipitate (probablya basic peroxidic nitrate) was separated from the supernatant solution.Radioactive analyses of the original solution and of the nal supernatantsolution showed that 99% of the plutonium was carried by the thoriumperoxide precipitate.

The use of a carrier precipitate to separate tetravalent plutonium froman aqueous solution, leaving hexavalent uranium in the supernatantliquid, is illustrated by the following example.

Example 11 Orthophosphoric acid was added to a nitric acid solution ofuranyl nitrate containing lanthanum nitrate, zirconium nitrate, andtetravalent plutonium, to form a solution 3 N. with respect to nitricacid, 0.36 M. with respect to phosphoric acid, containing approximately250 g. per liter of uranyl nitrate hexahydrate, and having a lanthanumion concentration of 0.1 g. per liter and a zirconium ion concentrationof 0.2 g. per liter. The resulting zirconium phosphate precipitate wasseparated from the supernatant solution, and both were subjected toanalysis for total alpha radiation. The total alpha radiation in eachcase was corrected for uranium alpha radiation on the basis of anotherprecipitation from a solution which contained no plutonium. The resultsshowed approximately 99% carrying of plutonium by the zirconiumphosphate precipitate with negligible carrying of uranium.

The use of a carrier precipitate to separate plutonium from an aqueoussolution, leaving uranium iission products in the supernatant solution,is illustrated by the following example.

Example 12 To an aqueous sulfuric acid-nitric acid-sodium iodatesolution containing tetravalent plutonium and beta-active fissionproducts in tracer concentrations thorium ion was added in aconcentration of about 17 mg. per liter. The

mixture was heated for a short time at a temperature below the boilingpoint, cooled, allowed to stand at room temperature for one-half hour,and filtered to separate the thorium iodate precipitate. The filtratewas evaporated to about one-half its original Volume and was then cooledand filtered to recover a second thorium iodate precipitate. Analysesfor alpha and beta radiation showed that the combined thorium iodateprecipitates contained all of the plutonium which was present in theoriginal solution but only about 4% of the beta-active fission products.

The use of a carrier precipitate to separate plutonium from an aqueoussolution, leaving neptunium in a higher oxidation state in thesupernatant liquid, is illustrated by the following example.

Example 13 A 4.3 M. sulfuric acid solution was prepared, containinglanthanum sulfate in a concentration of approximately 430 mg. per literand plutonium and neptunium in tracer concentrations. To this solutionwas added about 2.1 times its volume of an aqueous solution 0.2 M. withrespect to bromate ion and 0.2 M. with respect to bromine. The resultingsolution, which had a lanthanum sulfate concentration of about 139 mg.per liter, and was about 1.4 M. with respect to sulfuric acid, about0.14 M. with respect to bromate ion, and about 0.14 M. with respect tobromine, was allowed to stand at room temperature for two hours toeffect oxidation of the neptunium to the hexavalent state while leavingthe plutonium in the tetravalent state. About 27% by volume of 48%aqueous hydrofluoric acid was then added to the solution, and theresulting lanthanum uoride precipitate was separated by centrifuging.Analyses for alpha and beta radiation showed that the precipitatecontained 99% of the plutonium which was present in the originalsolution, but only 0.74% of the neptunium.

The following example illustrates the use of a radioactively inertdiluent or hold-back carrier to decrease the amount of a radioactivecontaminant carried by a plutonium-carrying precipitate.

Example 14 A 1.0 N. HNO3-0.5 N. HF solution was prepared, containingtracer concentrations of tetravalent plutonium and radioactivezirconium. Lanthanum nitrate hexahydrate was added to this solution in aconcentration of approximately 390 mg. per liter. The resultinglanthanum uoride precipitate was separated and subjected to radioactiveanalysis to determine its plutonium and zirconium content.

To a second portion of the HNOa-HF solution of plutonium and radioactivezirconium, inactive zirconium was added in a concentration of l g. perliter to serve as a diluent or held-back carrier. Lanthanum fluoride wasthen precipitated from the solution in the same concentration as before,and the precipitate was subjected to radioactive analysis to determineits content of plutonium and radioactive zirconium.

It was found that the lanthanum uoricle precipitate in each casecontained approximately 98% of `the original plutonium. The precipitatefrom the solution to which inactive zirconium had been added was foundto contain only j/30 as much radioactive zirconium as the precipitatefrom the other solution.

The following example illustrates the direct precipitation of .aninsoluble plutonium compound, without a carrier, from a ysolutionderived from a preceding carrier precipitate.

Example l5 A mixture :of hydroxides comprising 88.2% by weight oflanthanum hydroxide, 9.9% plutonium hydroxide and 1.9% potassiumhydroxide, Was dissolved in 2.03 times `its weight of 16 N. nitric acid.Approximately 13.22% by weight lof concentrated sulfuric acid (sp. gr.1.84) was added to the resulting solution, which was then diluted withwater to form a .solution 0.8 N. with respect to nitric acid and 0.2 N.with -respect to sulfuric acid. The plutonium concentration of thissolution was 8.25 g. per liter. The solution was heated to 60 C. and 50%by volume of 30% laqueous hydrogen peroxide was added over a period .ofone hour. The resulting slurry was digested for an additional hour atroom temperature, after which the plutonium peroxide (probably a basicperoxidic sulfate) was separated by filtration. The precipitate was thendissolved in 16 N. nitric acid, sulfuric acid was added, and thesolution diluted to 0.8 N. HNO3-0-2 N. H2504. Plutonium peroxide wasthen reprecipitated and separated by `filtration as before. Thereprecipitated product, which was free from lanthanum, amounted to 99%of the plutonium originally present in the lanthanum hydroxide mixture.

It should be understood, of course, that the above ex- -amples aremerely illustrative, `and do not limit .the scope of this phase of thepresent invention. Other plutonium carriers and hold-back carriers ofthe classes previously dened may be substituted for the particularcarriers used in the examples, and the procedures employed may be variedin numerous respects within the scope of t-he foregoing description.

Another aspect of the present invention relates to fu-r- .ther methodsfor the separation of plutonium from solutions thereof.

An object of this phase of the invention is to provide electrolyticmeans for the separation of plutonium fr-om solution.

Another object of this aspect of the present invention is to providesuitable methods for the electrodeposition of plutonium from solutionsin hydroxy solvents.

A further object is -to prov-ide means for simultaneouslyelectrodepositing plutonium and a carrier therefor from dilute solutionsof plutonium in aqueous or other hydroxy solvents.

Additional objects and .advantages of this phase of the presentinvention will be apparent from the following description.

Plutonium is a strongly electropositive metal, not far below the alkalimetals in the electromotive series, and it is therefore diicult toeffect electrodeposition of metallic plutonium. We have found, however,that plutonium may readily be electrodeposited las an oxygenatedcompound by the electrolysis of -suitable solutions of plutonium inhydroxy solvents. If the plutonium is present in solution Iin very lowconcentration, it may be electrodeposited simultaneously with theelectrodeposition of a carrier. Elect-rodeposition may thus be used inplace of or in conjunction with the precipitation methods or carrierprecipitation methods for vthe separation of plutonium which havepreviously been described.

Solutions from which plutonium may be electrodeposited in .accordancewith the present invention preferably contain plutonium in the form ofplutonyl ion, PuO2++, which may be reduced at the cathode to yield ahydrous oxide substantially insoluble under the conditions ofelectrolysis, or in the form of .a cation which will hydrolyze to aninsoluble compound in the layer of solution of low hydrogen ionconcentration immediately adjacent to the cathode. All of the commoninorganic salts of plutonium 'are readily hydrolyzable and may Isuitablybe employed in the present process. The plutonium in the electrolyte mayinitially be in any of its valence states or in an equilibrium mixtureof different valence states, and will be electr-odeposited, either byanodic oxidation to PuO2++ with subsequent cathodic reduction, or byhydrolysis to a compound substantially insoluble in t-he solution of lowhydrogen ion concentration in the immediate neighborhood of the cathode.

1The solvent may suitably comprise any normally liquid hydroxy solvent,but is preferably an aqueous solvent or `a lower aliphatic monohydricalcohol. Aqueous Ialcoholic solutions may be employed, if desired, butthe alcohols are suitably used as anhydrous solvents. Anhydrous ethylalcohol is the preferred solvent of the latter class.

When employing an anhyd-rous solvent, a desirably high conductivity maynot be obtainable without providing an auxiliary solute. This isespecially true in the case of a very dilute plutonium solution. In.such instance-s, a convenient way to increase the conductivity of thesolution, and also to facilitate the subsequent handling of theelectrode deposit, is to incorporate into the solution a compound of acarrier element which will electrodeposit simultaneously with theplutonium. Such compound may suit-ably :be any metal compound `which isnot substantially less hydrolyzable than the plutonium compound in ythesolution. The codeposition of plutonium and a carrier may be combinedwith preceding or following carrier precipitation processes .by thechoice of a suitable carrier cation which may be either precipitated orelectrodeposited from the solutions in quest-ion.

Aqueous solutions for the electrodeposition of plutonium may suitably beacidiiied in order to provide adequate conductivity. If the desiredplutonium concentration in the electrolyte exceeds 4the solubilityconcentration of plutonium hydroxide, or of a basic plutonium salt ofone of the anions in the solution, the pH should be lowered in order toprevent precipitation of the plutonium. Incrganic acid solutions ofabout 0.1 N.-l.0 N. are generally satisfactory for this purpose.Considerably higher acid concentrations may cause the formation ofnegatively charged complex ions, with resulting anodic deposition. Fordeposition only at the cathode, it is preferred to employ solutionshaving acid concentrations not substantially greater than 1 N.

Plu-tonium may be codeposited with a carrier from aqueous solutions inaccordance with the principles discussed above with reference toanhydrous solutions. From either type of solution of a hydrolyzableplutonium com-pound, plutonium will codeposit with an element which ispresent in the solution in the form of a compound which is notsubstantially less hydrolyzable than said plutonium compound.Conversely, `the plutonium may be deposited with at least partialdecontamination with respect to less easily hydrolyzable compounds ofcontaminating elements. Additional decontamination may be secured by apredeposition of metallic deposits of `the less electropositivecontaminants at potentials below ythe deposition potential for plutoniumin the particular solution.

Any of the common expedients employed in the electrodeposition art maybe applied to the electrodeposition of plutonium in `accordance with thepresent invention. The electrodes may be constructed of any conductingmaterial which is inert with respect to its surrounding electrolyteunder the deposition operating conditions. Although carbon or othernon-metallic electrodes may be used, metallic electrodes, and especiallymetallic electrodes having :amorphous surfaces, are generally preferred.The electrodes may be of any suitable shape, and may be fixed, rotated,or otherwise moved in the electrolyte as desired.

The operating potential and electrode spacing should be correlated, inconformity to the conductivity of the particular solution employed, toproduce as high a current density as is compatible with satisfactoryplutonium deposition. With anhydrous solutions the current density may-suitably range from 0.1 milliampere to 100 milliamperes or 4more persq. cm. of cathode surface; and with aqueous solutions the currentdensity may range from 1.0 milliampere to 1.0 ampere or more per sq. cm.of cathode surface.

The electrodeposition may be effected over .a considerable range oftemperature, from ordinary atmospheric temperatures to temperaturessubstantially below the boiling point of the solution employed.Temperatures of l0- 60 C. will generally be satisfactory, but we usuallyprefer l to effect the electrodeposition at a temperature of 20-30 C.

At .the conclusion of the electrodeposition, the electrodes should, ofcourse, be removed promptly from the electrolyte to prevent re-solutionof the deposit or attack of the electrodes by the electrolyte. Theplutonium deposit, or the codeposit of plutonium and carrier, may thenbe removed from its elect-rode by any suitable means, such as byscraping or other mechanical means, or by the use of an acid or othersolvent to form a solution for further processing.

The following examples illustrate the separation of plutonium fromaqueous and alcoholic .solutions by electrodeposition:

Example 16 Example 17 A `solution of lanthanum chloride in absolutealcohol, having a lanthanum chloride concentration of about 120 mg. perliter, and containing plutonium in tracer concentration, Waselectr-olyzed for a period of one hour at a potential of 50 volts,utilizing a platinum anode and a silver cathode. The initial cathodecurrent density was 1.0 milliampere per sq. cm. and the iinal currentdensity was 0.3 milliampere per sq. cm. of cathode surface.

The lanthanum and plutonium plated out together on the cathode afsoxygenated compounds, probably basic chlorides containing alcohol ofsolvation. Radioactive analysis of the plate and of the residualsolution showed that all of the plutonium had been plated out.

It is to be understood, of course, that the `above examples are onlyillustrative, and do not limit `the scope of this phase of the presentinvention. Other solvents, plutonium compounds, and carriers may besubstituted for the particular materials employed in the examples, andthe electrolyzing conditions may be otherwise varied in numerousrespects within the `scope lof the foregoing description.

A further aspect of Ithe present invention relates to the .separation ofcontaminating elements from plutonium and especially to the removal ofradioactive uranium ssion products from aqueous solution-s of plutonium.

An object of this phase of the invention is to provide 1a suitableprocedure for the separation lof contaminating elements from aqueoussolutions of plutonium While maintaining the plutonium in solution.

Another object of this phase of the present invention is to provideprecipitation methods for the separation of uranium fission productsfrom aqueous solutions containing plutonium and uranium fissionproducts, while maintaining the plutonium in solution.

A further object is to provide combination precipitation methods wherebyplutonium in aqueous solutions containing contaminating elements may bedecontamilnated by alternately precipitating cont-aminating elementswhile maintaining plutonium in solution and precipitating plutoniumwhile maintaining contaminating elements in solution.

Other objects and advantages of this aspect ofthe present invention willbe apparent from the following description.

When plutonium is removed from an aqueous solution by ymeans of aninsoluble carrier a certain proportion of the contaminating elementspresent in the solution will be carried along with the plutonium. If theseparation is made by precipitation of a carrier from a solutioncontaining large amounts of radioactive uranium fission products, theprecipitate may readily be suicien-tly radioactive as to requirehandling by remote control. Repeated redissolving and re-precipitatingwill result in further purication, land the decontamination can be stillfurther improved by the use of hold-back carriers, as has previouslybeen pointed out. The ultimate decontamination -of plutonium by such aprocess, however, is tedious and expensive, and it is desirable toemploy a more rapid and efficient method.

In accordance with the present invention, it has been `found thatrelatively rapid decontamination may be effected by maintaining theplutonium in an aqueous solution in a non-carryable state, whilecontacting the solution with ya carrier for one or more of thecontaminating elements present in the solution. Preferably the plutoniumis maintained in solution as an ion which forms a soluble compound withthe anion of the carrier, Whereas the carrier anion is capable -offorming insoluble compounds with contamina-ting cations present in thesolution.

In .the preferred modification of this phase of the pres-ent invention,the plutonium is maintained in solution in the hexavalent state whileprecipitating a carrier lfor the contaminating cations. The carrier forthis procedure may suitably comprise a carrier for trivalent ortetravalent plutonium, and such a carrier is highly advantageous whenemployed alterna-tively as a carrier Afor reduced plutonium and as acarrier for contaminants from a solution containing oxidized plutonium.ln such a combination procedure, contaminants which were carried withreduced plutonium in one 'step of the process may -be car-` ried awayfrom oxidized plutonium in a succeeding step employing the same carrier.Conversely, contaminants which would be carried with reduced plutoniumon a given carrier may first be carried, on that carrier, away fromoxidized plutonium.

The term carrierf as used herein with reference to the carrying ofcontaminants, is employed in the same sense previously used withreference to the carrying of plutonium. 4In both cases a carrier may beconsidered to be a substantially insoluble, solid, finely dividedcompound -capa'ole of ionizing to yield at least one inorganic cationand to yield at least one anion which constitutes an ionic component ofa compound which contains the ion to be carried, said latter compoundbeing not substantially more soluble than said nely divided compound inthe same solution. Taking lanthanum fluoride as an illus- -trativecarrier, it rnay *be seen that the fluoride anion c011- stitutes anionic component of a soluble compound of hexavalent plutonium, plutonylfluoride, and au ionic component of insoluble compounds of variousuranium lission products, e.g., uorides of radioactive lanthanum and ofyttrium, cerium, and other rare earths. Similarly, the phosphate anionof a zirconium phosphate carrier constitutes an ionic component of asoluble compound of hexavalent plutonium, plutonyl phosphate, and anionic component of insoluble compounds of various uranium fissionproducts, e.g., phosphates of radioactive zirconium and of strontium,yttrium, etc.

As has previously been pointed out, general decontamination may lbeeffected by the use of any of the carriers which are -suitable forcarrying `trivalent or tetravalent plutonium. Improved decontaminationwith respect to a specic contaminant however, may be effected by thechoice of a carrier 4cation which is isotopic or isomorphic Wi-th thecontaminating cation. In the case of a plurality of contaminants, suchas the uranium iission products, a plurality of different carriers maybe precipitated `simultaneously or successively from the same solutionof hexavalent plutonium. Such carriers may differ as to cation, as toanion, or as to both. When a plurality of carriers are precipita-tedsimultaneously, a convenient method is .to employ a plurality of cationswhich are precipitable by the same anion. Thus, the simultaneousprecipitation of lanthanum fluoride (La+3 ionic radius 1.06 A.) andceric iiu-oride (Ce+4 ionic radius 0:89 A.) lwill rem-ove two differentisomorphic series of contaminants.

`In order to carry contaminants from aqueous solutions of plutonium, anyplutonium which is presen-t in a carryable state is Ifirst oxidized to anon-carryable state. This is suitably acc-omplished by oxidizing any +3or +4 plu- .tonium to the +6 state in accordance with methods which havepreviously been discussed in detail in describing another phase of thepresent invention. 1n order to maintain the plutonium in the hexavalentstate during the contaminant carrying operation, an excess of oxidizingagent is generally incorporated in the solution. The resulting solutionis then contacted with the carrier in accordance with any of theprocedures which have previously been described with respect to the useof plutonium carriers. As in 4the case of plutonium carrying1 thepreferred procedure is Ito precipita-te the carrier in situ. The ionsmay be incorporated in the solution in any order, bu-t the cation isusually added first, followed by an excess of the anion. After digestionof the precipitate for a short time at room temperature, or at a'moderately elevated temperature, it is separated from the supernatantsolution by any convenient method such as decantation, iiltration, orcentrifuga-tion.

When using the preferred oxidation-reduction cycle of carrierprecipitations, a contaminant carrier may be employed which is identicalwith the plutonium carrier, or which differs from the plutonium carrieras to cation, as to anion, or as to both. Alternatively, two or morecontaminant carriers may be employed simultaneously or successively, onebeing the same as the plutonium carrier, or all being different from theplutonium carrier. It is generally `most convenient to employ at leastone carrier of the same chemical composition in both stages of theprocess. In such case, increased decontamination in the contaminantcarrier step may be secured, if desired, by the use of a combination ofa principal contaminant carrier of the same chemical ycomposition a-sthe plutonium carrier, together with smaller amounts of auxiliarycontaminant carriers termed scavengers The auxiliary carriers maysuitably be any carriers for the contaminants present in the solutionwhich may ,be precipitated from the same -solution from which theprincipal contaminant carrier is to be precipitated and which are notisomorphic with the principal contaminant carrier. When decontaminationwith -respect -to radioactive uranium `fission products is desired,suitable scavengers comprise insoluble compounds of radioactively inertisotopes of .the fission products. Such scavengers are convenientlyco-precipitated with the principal contaminant carrier. The principal`and auxiliary carriers may, however, be precipitated successively, inany order, from the oxidized plutonium solution.

The two stages of the oxidation-reduction carrier cycle may be carriedout in any order, i.e., the first carrying may be effected from anoxidized plutonium solution or from a reduced plutonium solution asdesired. if the first carrier is precipitated from an oxidized plutoniumsolution, the precipitate is separated and discarded, and the plutoniumin the supernatant solution is then reduced to a carryable state by anyof the methods which have previously been described. The plutoniumcarrier is then precipitated in the resulting solution. lf excess anionwas employed in precipitating the preceding contaminant carrier, and thesame compound is to be precipitated as the plutonium carrier, this maybe accomplished simply by adding the desired quantity of the carriercation. The plutonium-carrying precipitate is then digested in the usualmanner and separated from the supernatant solution. rThe precipitate issuitably redissolved in relatively strong mineral acid and the resultingsolution is then diluted to the desired concentration for subsequentprocessing. The plutonium in this solution may be reoxidized, andanother car-rier precipitation may be effected for further removal ofcontaminants. r.this oxidation-reduction cycle may be repeated as oftenas necessary to obtain the desired decontamination, and the quantity ofcarrier may be reduced in successive stages to achieve simultaneousconcentration of plutonium with respect to its carrier.

The following example illustrates decontamination by anoxidation-reduction carrier cycle:

Example 18 Plutonium was separated from the uranium and -fissionproducts contained in uranyl nitrate hexahydrate which had received 100milliarnpere hours neutron bombardment. The uranyl nitrate had beenstored for approximately four weeks after bombardment, and it containeda substantial amount of 94 Pu239 but was practically free from 93 Np239.The 94 Pu239 was separated by the following procedure:

Approximately 1053 parts by weight of the bombarded uranyl nitratehexahydrate described above, and approximately 30 parts by weight ofthorium nitrate dodecahydrate, were dissolved in sufiicient nitric acidto produce a solution 2 N with respect to nitric acid after the additionof 3186 parts by weight of a 0.35 M potassium iodate solution. Suiicientradioactive plutonium, 94 Pu238, was incorporated as a tracer to give ana count of 10,000 per minute per ml. of the final mixture. The potassiumiodate solution was then added, producing a solution having a uraniumconcentration of approximately 0.050 g. U per ml. This solution,containing the resulting thorium iodate precipitate, was allowed tostand for twenty minutes at room temperature.

The thorium iodate precipitate, containing the bulk of the plutonium,was then filtered ofi and washed with a solution 1.0 M with respect tonitric acid and 0.1 M with respect to potassium iodate. The washedprecipitate was dissolved in 1188 parts by weight of 12 N hydrochloricacid, 2198 parts by weight of 0.5 M sodium dichromate solution wasadded, and the resulting solution was then diluted With water to aconcentration 2.4 N with respect to hydrochloric acid and 0.1 M withrespect to sodium dichromate. This solution was then digested forone-half hour at 65 C. to effect oxidation of the Pu+4 to Pu+5.

The Pu+6 solution was then cooled to room temperature, after which 4248parts by weight of 0.35 M potassium iodate solution was added, and themixture was allowed to stand for twenty minutes at room temperature. Theresulting thorium iodate precipitate, containing the bulk of the fissionproducts, was tiltered ofi and washed in the same manner as the firstthorium iodate precipitate.

The distribution of the plutonium and fission products between the firstthorium iodate precipitate, the first supernatant liquid, the secondthorium iodate precipitate, and the second supernatant liquid, wasdetermined by measurement of the or, and ry radiation emitted. For thispurpose, blank determinations were first made on the original mixture,prior to the separation of the fist thorium iodate precipitate. The acount on this original mixture was taken to be that of the added 94Pu238. Aliquots were analyzed for total count, and for total countcorrected for the UXl count, by means of Geiger-Mueller counters andwell known techniques. Aliquots of the two thorium iodate precipitatesand of the two supernatant liquids were then analyzed for and yactivities in the same manner.

The plutonium content of the two thorium iodate precipitates and of thetwo supernatant liquids was recovered by an additional precipitation ineach case, and the a activity of each of the precipitates was thendetermined. Since 95 P11233 and 94 Pu239 have identical chemicalproperties, the distribution of 94 Pu238, as indicated by the a counts,also represented the distribution of the 94 Pum.

The distribution of uranium, plutonium, and fission 25 products obtainedby the above separation procedure is shown in the following table:

25 The centrifugates from the two iodate precipitates were combined andevaporated with concentrated hydrochloric The following exampleillustrates concentration of plutonium with respect to its carrier, aswell as decontamination, in an oxidation-reduction carrier cycle:

Example I 9 Lanthanum lluoride, carrying plutonium as the onlyalpha-active component, and carrying beta-active contaminants, wasdissolved in a mixture of nitric and sulfurie acids. The solution wasevaporated until fumes of sulfur trioxide were evolved and was thencooled and diluted with water to 30` times the volume of the fumingsolution. A mixture of potassium peroxydisulfate and silver nitrate in aratio of 20 to 1 was then added and the solution was digested forminutes to effect oxidation of the plutonium to the hexavalent state.Hydrofluoric acid was then added in a concentration in excess of theequivalent concentration of lanthanum ion. After digestion for 5 minutesthe lanthanum iluoride precipitate was separated by centrifuging.

The centrifugate was evaporated until fumes of sulfur trioxide wereevolved, thus destroying the peroxydisulfate and effecting reduction ofthe plutonium to the tetravalent state, and the solution was then cooledand diluted with Water. Lanthanum ion, an amount less than that in thepreceding precipitate, together with an excess of hydrouoric acid, werethen introduced. The resulting lanthanum iiuoride precipitate wasseparated by centrifuging, washed with dilute hydrotluoric acid, anddried.

The ratios of plutonium t0 lanthanum fluoride carrier in the initialmaterial and in the iinal precipitate were determined on the basis ofalpha radiation and weight of lanthanum. It was found that the ratio ofplutonium to carrier in the final precipitate was 131% of the ratio inthe initial material, whereas the ratio of beta contamination to carrierin the iinal precipitate was only 13% of the ratio in the initialmaterial.

The following example illustrates an oxidation-reduction carrier cycleutilizing simultaneous precipitation of two contaminant carriers, `oneof which contains the same cation element as the plutonium carrier andthe other of which diifers from the plutonium carrier as to both cationand anion.

Example A cerous fluoride precipitate carrying plutonium as the onlyalpha-active component, and carrying beta-active contaminants, wassubjected to radioactive analysis for total alpha and beta radiation.The precipitate was dissolved in nitric and sulfuric acids, the solutionevaporated to dryness, and the residue dissolved in aqueous nitric acid.An excess of potassium bromate was introduced and the bromate ion,catalyzed by cerium, oxidized the plutonium from the tetravalent to thehexavalent State. A substantial proportion of the cerous ion wassimultaneously oxidized t0 ceric ion. Thorium ion and an excess ofiodate ion were then introduced to precipitate mixed thorium and cericiodates. This precipitate was separated by centrifuging and wasdissolved and reprecipitated with additional thorium and iodate ions.

acid. The resulting solution was cooled, and sulfur dioxide wasintroduced to reduce the hexavalent plutonium. Hydroluoric acid was thenadded, and the resulting cerous uoride precipitate was separated bycentifuging, Washed with dilute hydroliuoric acid, and dried.

Radioactive analysis of the iodate precipitates showed them to beinactive with respect to alpha radiation, thus indicating no by-productloss of plutonium. Analysis of the iinal plutonium-carrying cerousfluoride precipitate showed it to contain only one third of the beta.radiation of the initial cerous fluoride precipitate.

The following example illustrates the separation of specificcontaminants from a plutonium solution by means of a carrierprecipitation:

Example 21 A lanthanum uoride precipitate carrying plutonium as the onlyalpha-active component, and a second lanthanum fluoride precipitatecontaining no alpha-active component and carrying UX1 and UY as the onlybeta-active components were subjected to radioactive analyses for alpharadiation and beta radiation.

he two precipitates were combined and dissolved in a mixture of nitricand sulfuric acids. The solution was evaporated until fumes of sulfurtrioxide were evolved, and was then cooled and diluted with water toabout 30 times the volume 0f the fuming solution. A mixture of potassiumperoxydisulfate and silver nitrate, in a ratio of 2() to l, was thenadded and the resulting solution was digested for 15 minutes to eiectoxidation of the plutonium to the hexavalent state. Hydrouoric acid wasthen added to the solution in a concentration in excess of theequivalent concentration of lanthanum ion. After digestion for tiveminutes, the lanthanum iluorine precipitate was separated bycentrifuging, and was then washed with dilute hydroiiuoric acid anddried.

The precipitate was subjected to radioactive analysis for alpha and betaradiation, and was found to contain at least 34.1 percent of theoriginal UX1 and UY but less than 0.34 percent of the originalplutonium.

It is to be understood, of course, that the above examples are not to beconstrued as limiting the scope of this phase of the present invention.Other Vequivalent carriers and operating procedures may be substitutedfor Ythe particular carriers and procedures of the examples,

in accordance with the foregoing general description.

A further phase of the present invention relates to improved methods forthe concentration and decontamination of plutonium, and particularly tomethods employing a plurality of plutonium carriers of differentchem-ical composition.

An object of this aspect of the invention is to provide a'multi-stagemulti-carrier process for the separation of plutonium from mixtures ofplutonium and contaminating elements.

Another object of this phase of the invention is to provide a processfor alternately carrying plutonium on car- Vriers of different chemicalcomposition, whereby the plutonium is concentrated with respect to itscarrier.

sas-)dana A further object is to provide a process for the separation ofplutonium from uranium iission products by a combination of plutoniumcarrier precipitations and lission product carrier precipitations,employing a plurality of plutonium carriers of different chemicalcomposition, whereby the plutonium is decontaminated with respect touranium ission products and concentrated with respect to its carrier.

Additional objects and advantages of this aspect of the presentinvention will be evident from the following description.

In accordance with one modification of this phase of the invention,plutonium is carried from an aqueous solution by means of a firstplutonium carrier, the carrier and its associated plutonium aredissolved to form a second aqueous solution, and plutonium is separatedfrom the second solution by means of a second carrier which differs inchemical composition from the first carrier. In such a processsuccessive plutonium carriers may be chosen which are non-carriers fordifferent contaminating elements, thus improving the decontaminationover that obtainable from the successive use of the same plutoniumcarrier. Thus, in the decontamination of plutonium with respect touranium fission products, the use of a plurality of non-isomorphicplutonium carriers will permit a plurality of different isomorphicseries of fission products to be separated with the differentsupernatant solutions.

The alternate use of different plutonium carriers also facilitates theconcentration or" plutonium with respect to its carrier. The ratio ofcarrier to plutonium may be successively decreased in each cycle of theprocess. Each carrier may be dissolved in a smaller volume of solutionthan that required for the preceding carrier; and a solution may nallybe obtained from which a plutonium cornpound may be precipitated withoutany carrier. Such concentration may be effected simultaneously withdecontamination, as in the recovery of plutonium from solutions orprecipitates containing uranium fission products. Alternatively, theconcentration may be applied to previously decontaminated solutions orcarrier precipitates, or for the recovery of plutonium from dilute wastesolutions, or the like.

The successive carriers in the present process may differ in cations orin anions or in both, and the cations may differ as to their chemicalelements or only with respect to the state of oxidation of the sameelement. In any case, however, the conditions for the precipitation of asubsequent carrier should be such that at least one of the ions of thepreceding carrier remains in solution. Since reduction in carrier ratioin successive cycles is diflicult in the case of common cations, orcommon cation elements, it is desirable to employ successive carriershaving different cation metals, and we prefer to employ combinations ofcarriers which ditier both in cations and in anions.

Although the carriers may be employed as pre-formed nely divided solids,it is preferable to precipitate the carrier in situ since the latterprocedure usually permits a lower carrier ratio and results in morequantitative carrying of plutonium. Substantially the same techniquesfor carrier precipitation may be employed in our multiple carrierprocess as have previously been described for single carrier procedures.In general, it is desirable to incorporate the carrier cation in thesolution, agitate while adding the carrier anion, and digest theresulting mixture prior to separating the precipitate.

Each precipitate is suitably dissolved in the minimum volume of solutionfrom which the subsequent carrier may be precipitated substantially freefrom the preceding carrier. The use of different solvents in succeedingstages will facilitate volume reduction, but the same solvent may beused if the concentrations are suitably adjusted. We generally prefer toemploy aqueous solvents and to modify their solvent power from stage tostage by adjustment of ionic concentrations. Thus, an aqueous solutionof an inorganic acid or base may be used as the solvent in successivestages of our process and the pH may be adjusted to increase the solventpower from stage to stage. Also, precipitation of a carrier in thepresence of a large excess of one of the carrier ions will permitredissolving in a smaller Volume of the same solvent in the I'absence ofsuch excess ion. Alternatively, an additional ion may be introduced toform a soluble complex Iwith the cation of the preceding carrier. Otherequivalent procedures for reducing the volume of .solution from stage tostage and tor precipitating a `carrier free from preceding carrier willbe evident to those skilled in the art.

The ratio of carrier to plutonium in the present process may vary over awide range depending on the plutonium concentration of the originalsolution and upon the effectiveness of the particular carrier employed.Ratios ranging from 10,000/1 or higher in the first stage of the processto 10/1 or lower in the nal stage may be used. However, the ratio willgenerally fall within the range 1,000/1 to 100/1.

After one or more carrier precipitations in accordance with the presentconcentration procedure, a nal precipitation may be made with asufciently low -ratio of carrier to plutonium so that the precipitatemay be dissolved in a small volume of solution and a plutonium compoundmay then be precipitated directly Without a carrier. If an isomorphiccarrier is employed in the final carrier stage of the process, it willbe necessary to change the valence state of the plutonium, or of thecarrier cation, in the linal solution in order to make a iinalprecipitation of a pultonium compound free from carrier. On the otherhand, if the linal carrier is non-isomorphic with plutonium it will onlybe necessary to select conditions for the nal precipitation of theplutonium compound such that at least the cation of the carrier remainsin solution.

This modication of the present invention will be further illustrated bythe following specific examples:

Example 22 A cerous fluoride precipitate carrying plutonium as the onlyalpha-active component, and carrying beta-active contaminants, was-analyzed for plutonium content by measuring its alpha radiation with aproportional counter, `and was analyzed for beta radiation by means of acalibrated electroscope.

The precipitate was dissolved in a mixture of nitric and sulfuric acidsby heating. Thorium ion and an excess of -iodate ion were introduced-into the h-ot solution. Thor-iam `iodate precipitated from the mixtureon cooling and was separated by centrifuging. Additional thorium wasintroduced `into the supernatant liquid, and the resulting secondthorium iodate precipitate was separated by tiltration. The ltrate wasthen evaporated to onehalf its original volume and cooled to form athird thorium iodate precipitate which was then separated by filtration.

The three thorium iodate precipitates were analyzed for alpha and betaradiation, land it was found that they contained percent of the original`alpha radiation, `and only 5 percent of the original beta radiation.This change to a carrier differing from the original carrier in bothanion and cation was then accomplished with quantitative recovery ofplutonium 'and with a 20 to 1 decontamination with respect to betaradiation.

Example 23 Orthophosphoric acid was added to a nitric acid solu- Itionof neutron bombarded uranyl nitrate hexahydrate containing lathanumnitrate and zirconium nitrate to form a solution 3 N with respect tonitric acid, 0.06 M with respect lto phosphoric acid, containingapproximately 114.5 g. of uranyl nitrate hexahydrate per liter, andhaving a lanthanum concentration of 0.03 g. per liter and a zirconiumconcentration of 0.1 g. per liter. The resulting zirconium phosphateprecipitate was separated and washed with 3 N HNOS-0.05 M H3PO4. Theprecipi- E@ tate was then dissolve-d in concentrated nitric acid,lanthanum nitrate and concentrated hydrotluoric acid were introduced andsufficient Water was added to form a solution 1.05 N with respect tonitric acid, 4.76 N with re- 30 tion in Ia concentration of about 90 mg.per liter, and excess `aqueous hydrofluoric acid was added toprecipitate lanthanum fluoride. The precipitate was then separated andwashed with dilute aqueous hydrouoric acid.

spect to hydroiluor-ic acid, and having a zirconium con- 5 The recoveryof plutonium through the above three centration' of 0.066 g. -per literand a lantlianurn constage carrier precipitation process was found to be92 centration of 0.02 g. per liter. The resul-ting lanthanum percent ofthat obtainable in .a single stage process fluoride precipitate was thenseparated from the superemploying lanthanum fluoride as the carrier. Thedeconnatant solution and Washed with dilute hydrofluoric acid.tamination with respect to gamma-active uranium fission The plutoniumconcentrations of the initial solution product-s obtained in the .threestage process was deterand of the fin-al precipitate were determined byalpha mined by measuring the total gamma radiation of variradia-tionmeasurements and `it'was found that at least ous fractions throughout.the process. The distribution 86 percent of the initial plutonium wasrecovered in the of the gamma radiation was found to be as follows: nallprecipitate. The ratio of weight of plutonium .to weight of carrier in.the final precipitate was increased l5 Fraction: Percent ,of totalgamma radiation by a concentration factor of. 6.6 over the ratio in theOriginal solution 100.0 first carrier precipitate. y Fir t e t t lut. 445 The degree of decontamination with respect to gamina- ,S s Sup ma anso '110.11 active uranium fission products was determined by meas-Eicond supernatant so .umm 8'5 Final `supernatant solution 40.0 uringthe total gamma radiation of the initial, internie-` Final precipitate7.0 diate, and final materials. The distribution of the gamma T 1 g 0-5radiation was found .to be as follows: Qta 10 Fraction: Percent loftotal amma radiatioi g l The :above results illustrate the inefficiencyof decon- Original solution 100.0

n tamination by .repeated use of the `saine carrier as com- Ftfssupefllaan Soulfm e- 64-3 pared to the alternate use of carrires ofdifferent chem- Final supernatant solution 33.0 cal compsitiol FinalPfillPltae 2-7 Vr'Additional examples of suitable alternate .carriercom- Total 100.0 biniati'ons are shown in the following table:

TABLE 8 Preoedng solution Carrier precipitate Subsequent solutionSubsequent carrier Final solution precipitate LaF3 (ZrO)3(PO4)2 Aq IEfClItalia" H LaPOi LaPOl Le C2o CeF CePO4 Ai 0H L Fe oH)3 Cu(oi)2.

OLKFZ Uolxrno- (ZIOMPOOi (ZIOMPODi- Th(l03)4 *Followed by reduction ofPuOZ+2 to Put-4.

Example 24 An aqueous solution, yabout 0.36 N with respect to hydrogenperoxide and about 0.45 N with respect to arnrnonium ion, was preparedfrom neutron irradiated uranyl nitrate Ihexahydrate. The uraniumconcentration was approximately47-4 g. per liter (100 g. of hexahydrateperliter), and the solution contained La+3, Ba+2, and ZrO+2 -ashold-back carriers in concentrations of 0.2 g. per liter. The ipH of thesolution was adjusted to 2.6 by means of ammonium hydroxide, and theresulting uranium peroxide precipitate (probably a basic peroxidicuranium nitrate) was separated from the supernatant solution and Washedwith dilute aqueous hydrogen peroxide.

The decontamination obtainable in the alternate carrier processdescribed above may be substantially improved by the use of one or morecontaminant carrying steps between successive plutonium carrying stepsof the cycle. Thus, in decontaminating plutonium with respect to uraniumfission products, a plutonium carrier is suitably precipitated from adilute solution of plutonium and fission products; the precipitate isredissolved to form a second solution; at least one fission productcarrier is precipitated and separated from this solution; and a secondplutonium carrier, differing in chemical composition from the firstplutonium carrier, is then precipitated and separated from the solution.Simultaneous concentration of plutonium may be secured in this processin the sanie manner as in the process employing no interveningcontaminant carriers, i.e. by successively reducing carrier ratios andsolution volumes.

In this modification of the present process, the intervening fissionproduct carriers may be the same as one or both of the plutoniumcarriers, or may be chemically distinct from both of the plutoniumcarriers. From the standpoint of decontamination, it is generallydesirable to follow a plutonium carrier with the same carrier, or `oneisornorphic therewith, as a fission product carrier.

Conversely, more complete decontamination may be secured in the finalplutonium-carrying precipitation of the cycle if the plutonium carrieris isomorphic with the plutonium compound to be carried but is notisomorphic with the preceding fission product carrier. However, if twointervening fission product carriers are employed, it is generally moreconvenient to use the same carriers as the preceding and subsequentplutonium carriers.

In order to employ the same compound successively as a plutonium carrierand as a fission product carrier, conditions must be employed whichprevent the carrying of plutonium in the fission-product-carryingprecipitation. This may conveniently be accomplished 4by changing thestate of oxidation of the plutonium in the manner previously describedfor oxidation-reduction cycles with a single plutonium carrier.

In the preferred process of this phase of the present invention, theplutonium is carried in the +4 valence state and is maintained insolution in the +6 valence state while carrying fission products, Inaccordance with one modification of this process, an operating cyclecomprises the precipitation of a carrier for +4 plutonium, solution ofthe precipitate, oxidation of the plutonium to the +6 state,precipitation of a fission product carrier which may -be the same as, ordifferent from, the preceding plutonium carrier, reduction of theplutonium to the +4 state, precipitation of a second plutonium carrierchemically distinct from the first plutonium carrier, and solution ofthe second precipitate to form a smaller volume of solution than thatresulting from the dissolution of the first precipitate.

This modification of the present invention will be further illustratedby the following specific example.

was evolved. The resulting solution which had a thorium concentration ofabout l g. per liter, was diluted with about 3() times its volume ofwater, and potassium peroxydisulfate and a trace of `silver nitrate wereadded, together with lanthanum ion to a concentration of about 32 mg.per liter. The solution was then warmed and digested for one-half hourto effect oxidation of the plutonium Ito the hexavalent state.Hydrouoric acid in excess of the equivalent lanthanum concentration wasthen added and the resulting lanthanum fluoride precipitate, with itsassociated ssion products, was separated by centrifuging.

The centrifugate Kwas heated for one hour below the boiling point andwas then evaporated until sulfur trioxide fumes were evolved thuseffecting reduction of the 'hexavalent plutonium. The resulting solutionwas cooled and diluted with water, and lanthanum -ion =was introduced inan amount equal to that employed in the preceding precipitation.Hydrofluoric .acid in excess -of the equivalent lanthanum concentrationwas then added, 'and the lanthanum fluoride precipitate, with itsassociated plutonium was separated by centrifuging.

f Radioactive analyses of the initial and subsequent precipitates showedthat the lanthanum fluoride precipitate from the oxidized plutoniumsolution contained less than 3 percent `of the plutonium which waspresent in the initial `thorium iodate precipitate, Whereas the finalplutonium-carrying lanthanum fluoride precipitate contained less than 14percent of the beta-active ission products which were present in theoriginal thorium iodate pre- 0 cipitate.

TABLE v9 Preeeding solution First plutonium carrier precipitateMetathesizing agent Subsequent solution Oxidizing agent Th(C204)z ThFLaz(CzO4)3 Ce(IOa)4 CeF LaF1 (ZrO)a(PO4)2 radom Example 25 A thoriumiodate precipitate carrying plutonium as the only alpha-activecomponent, and carrying beta-active fission products, was dissolved inconcentrated hydrochloric acid. Concentrated sulfuric acid was added and.the solution was evaporated until sulfur trioxide fumes were evolved.Concentrated nitric acid was then added In the preferred modification ofthis phase of the present invent-ion two or more fissi-on productcarriers of different .chemical composition are employed between thefirst and second plutonium carriers yof the cycle. In this mannermaximum decontamination as well as maximum concentration may beaccomplished in a single cycle of the process. Sui-table carriercombinations for two -ission and the solution was again evaporated untilsulfur trioxide 75 product carrier precipitations between the iirst andsecond

1. A PROCESS FOR THE PRODUCTION OF PLUTONIUM WHICH COMPRISES SUBJECTINGA MIXTURE OF U238 AND A FISSIONABLE ISOTOPE TO A SELF-SUSTAININGNEUTRONIC CHAIN REACTION, AGING THE REACTED MATERIAL, THE COMBINED TIMEOF REACTION AND AGING BEING SUFFICIENT TO PRODUCE A TOTAL TRANSURANICFRACTION COMPRISING AT LEAST 90 PERCENT PLUTONIUM, AND SEPARATINGPLUTONIUM FROM THE AGED REACTED MATERIAL.